The invention relates to an apparatus for inductively transmitting power, which apparatus comprises a primary unit with a primary coil and a secondary unit with a secondary coil and in which the primary coil generates a magnetic transmission field in a transmission area between the primary unit and the secondary unit.
Inductive power transmission systems are known from the prior art. For example, the document FR 2 947 114 A1 describes an inductive charger for a vehicle for charging an electrical, energy store of the vehicle. The inductive charger consists of a ground unit with a primary coil and a vehicle unit with a secondary coil. The distance between the two coils is approximately 0.1-0.2 m.
An inductive charger for an electric vehicle is designed to transmit power in the range of several kilowatts.
An object of the invention is to describe an improved apparatus for transmitting energy.
This object is achieved by means of an apparatus according to claim 1. Advantageous embodiments and developments of the invention emerge from the dependent claims.
According to the invention, the apparatus has an even number of detector coil elements, wherein the detector coil elements being wound in opposite directions in pairs and forming a detector pair for detecting an induction voltage.
Within the scope of this disclosure, “wound in opposite directions” means that, if the detector pair is permeated with a homogeneous, ideal magnetic field, a voltage is respectively induced in the two detector coil elements and these two voltages have opposite polarity.
According to another variant of the invention, the detector pairs are electrically connected to one another in at least one series circuit, the at least one series circuit forms at least one detector unit, at least one measuring means for measuring an induction voltage at the detector unit is assigned to the at least one detector unit, and the at least one detector unit can be introduced or has been introduced into the transmission area.
The voltages induced with opposite polarity in a detector coil pair are connected in series. Consequently, the voltages are at least partially compensated for over the entire detector coil pair. If the two detector coil elements are structurally identical apart from the winding in opposite directions and if the permeating magnetic field is homogeneous, the total voltage induced by the detector coil pair is zero. This also applies to a plurality of detector coil pairs which are again connected in series with one another and form a detector unit.
It is particularly advantageous if the at least one detector unit is de-energized or the induction voltage is low in the case of a homogeneous transmission field, and the induction voltage is increased at the at least one detector unit in the case of an inhomogeneous transmission field.
If the magnetic field permeating the detector pair is inhomogeneous, the total voltage induced by the detector pair or by a plurality of detector pairs differs from zero. If the further detector pairs of the detector unit are also permeated by a homogeneous field, the total voltage induced by the detector unit likewise differs from zero. This makes it possible to determine inhomogeneities of a magnetic field which is homogeneous per se. The apparatus preferably has a plurality of detector units in the transmission area, which detector units cover the entire transmission area in a manner perpendicular to the orientation of the transmission field.
According to another variant of the invention, the at least one detector unit can be moved within a movement range perpendicular to the orientation of the transmission field in the transmission area, the movement range covering the transmission area.
The transmission field can therefore be scanned for local inhomogeneities using the detector unit.
In this case, an increased induction voltage of a detector unit is sufficient to determine a local inhomogeneity in the transmission field.
It is particularly advantageous if the spatial extent of a detector coil element is adjustable.
If a local inhomogeneity of the transmission field assumes approximately the magnitude of the spatial extent of a detector coil element instead of the detector unit, the induction voltage of the relevant detector pair is particularly pronounced. This means that the detector unit is particularly sensitive in this case. The sensitivity of the detector unit can therefore be optimized with respect to the magnitude of the spatial extent of the local inhomogeneity.
A system having the apparatus and having a vehicle in order to inductively transmit power to the vehicle is preferred, the secondary unit being included in the vehicle and being situated in the region of the underbody of the vehicle, the primary unit being situated outside the vehicle, and the at least one detector unit being included in the primary unit or the secondary unit.
Metal objects situated in the transmission area can be detected using the detector unit while transmitting power to the vehicle.
This means that high magnetic field strengths prevail in the space between the coils.
The invention is based on the considerations explained below:
With respect to inductive systems for transmitting power, for example for charging a vehicle with an electrified drive train, there are currently no systems which detect metal objects in the transmission path in a cost-effective and reliable manner. Optical systems, for instance an infrared camera, can be easily contaminated and detect heating of the metal object only if the metal object is not covered by a neutral body. Ultrasound systems with suitable dimensions detect all objects which are sufficiently large in relation to a vehicle. Small or flat Objects (for example coins) are not detected. They even reduce the availability under certain circumstances since non-metal objects are possibly also detected as metal objects. A conventional metal detector, as known from geology for instance, suffers from interference from the magnetic and metal objects in the system and from the very strong transmission field when charging an electric vehicle, for instance, and should therefore be integrated in a complicated manner.
When using a conventional metal detector, it is necessary to generate a detection magnetic field in addition to the magnetic field which transmits the energy. This requires additional effort. This field does not follow the geometry of the transmission field. Therefore, there is insufficient coverage of the monitored area with the danger area.
It is therefore proposed to use the existing energy transmission field as excitation. Detection is carried out using a special configuration of the sensor coils and adapted evaluation, of the signals. The method is particularly suitable for parts which are very small in relation to a vehicle, for example a coin. Very large metal foreign objects can be detected via a changed energy transmission behavior.
Such a system is also robust and reliable.
One preferred exemplary embodiment of the invention is described below using the accompanying drawings. Further details, preferred embodiments and developments of the invention emerge from the drawings.